Semiconductor wafers are processed in wafer processing systems. An example conventional wafer processing system will now be described with reference to FIGS. 1 and 2.
FIGS. 1 and 2 illustrate a conventional wafer processing system. In the figures, wafer processing system 100 includes a confinement chamber portion 102, an electrode 104, an electrostatic chuck (ESC) 106, an electrode driving source 112, an ESC driving source 114 and a pin lifting system 116. Confinement chamber portion 102 has an input portion 108 and an output portion 110. Pin lifting system 116 includes a lifting pin 118. Confinement chamber portion 102 surrounds a processing space 122 used to process a semiconductor wafer 120.
In operation, as illustrated in FIG. 1, semiconductor wafer 120 is disposed onto ESC 106. ESC driving source 114 applies a voltage to ESC 106, thereby creating an electric field, which creates a Coulomb force that holds semiconductor wafer 120 onto ESC 106. While semiconductor wafer 120 is held in place by ESC 106, a plurality of materials may be supplied to processing space 122 via input portion 108, while a voltage is applied to electrode 104 via electrode driving source 112 to create plasma within processing space 122. The created plasma within processing space interacts with semiconductor wafer 120, either by etching portions of semiconductor wafer 120, or by depositing material onto semiconductor wafer 120. When the process is complete, the remaining material within processing space 122 is removed via output portion 110. Second driving source 114 then stops applying a voltage to ESC 106, which terminates the Coulomb force, which then releases semiconductor wafer 120. As illustrated in FIG. 2, pin lifting system 116 then pushes up on semiconductor wafer 120 to relieve the surface tension, lifting one edge of semiconductor wafer 120 off of ESC 106. Semiconductor wafer 120 is then removed from wafer processing system 100.
Great care must be taken in both construction and utilization of wafer processing system 100 in order to maintain the precision required in all aspects of semiconductor wafer processing. ESC 106, in particular is a very expensive portion of wafer processing system 100. The operational parameters of ESC 106 must be precisely maintained in order to accurately hold and release semiconductor wafers. Non-limiting examples of operational parameters of ESC 106 include surface resistance, surface capacitance and overall impedance, each of which may be changed as a result to changes, or damage, to the physical integrity of ESC 106. As such, ESC 106 may not function efficiently, or even at all, if its physical integrity is degraded.
ESC 106 is specifically susceptible to damage from lifting pin 118, as will be described below with respect to FIGS. 3 and 4.
FIG. 3 is an exploded view of portion A of FIG. 1. In FIG. 3, lifting pin 118 is separated from the inner wall of ESC 106 by a radial distance 302. The separation is needed to eliminate contact between lifting pin 118 and ESC 106 thereby preventing damage to ESC 106 from lifting pin 118.
FIG. 4 is an exploded view of an example situation of portion A, when lifting pin 118 is moved closer to semiconductor wafer 120. In the figure, the longitudinal axis of lifting pin 118 should align perpendicularly with ESC 106, along line 402. However, in this example situation, the longitudinal axis of lifting pin 118 is actually aligned along line 404, which is separated from the axis along line 402 by an angle θ. Because the longitudinal axis of lifting pin 118 is aligned along line 404, when lifting pin 118 moves close to semiconductor wafer 120, lifting pin 118 contacts ESC 106 at point 406. As lifting pin 118 continues to rise toward semiconductor wafer 120, pin continues to scrape against ESC 106. Such scraping may damage ESC 106, which may change the physical integrity of ESC 106, which may change operational parameters of ESC 106, and which may result in ESC 106 functioning inefficiently or improperly. In such an event, ESC 106 must be repaired or replaced, either of which is costly.
A more detailed description of a conventional pin lifting system will now be described with reference to FIGS. 5 and 6.
FIG. 5 illustrates conventional pin lifting system 116 in a first state. As seen in the figure, pin lifting system 116 includes lifting pin 118, a pin holding shaft 504, a housing neck 506, a housing outer portion 508, a first bearing 510, a bearing separating portion 512, a second bearing 514 and a bellows portion 516. Bearing separating portion 512 separates first bearing 510 from second bearing 514 and additionally has a window 518 cut therein. Window 518 enables a lifting arm (not shown) to lift pin holding shaft 504 via notch 520. Pin holding shaft 504 includes a pin holding portion 522, an intermediate portion 524, a seat portion 526 and an end portion 528, which includes notch 520. Housing neck 506 includes a shaft guiding portion 532, a cap portion 534 and an inner portion 536. Housing outer portion 508 includes a lip portion 530.
Pin lifting system 116 is mountable into ESC 106 in a mounting hole 540. Mounting hole 540 includes a neck portion 542, a pin portion 544 and pin opening 546 at the top surface of ESC 106. Neck portion 542 is designed to pass lifting pin 118 and to retain shaft guiding portion 532. Pin portion 544 is operable to pass lifting pin 118, whereas pin opening 546 is designed to pass the tip of lifting pin 118. A fastening plate 548 retains pin lifting system 116 within mounting hole 540.
Cap portion 534 is connected to housing outer portion 508. One end of bellows portion 516 is connected to inner portion 536 of housing neck 506, whereas the other end of bellows portion 516 is connected to seat portion 526. First bearing 510 is connected to lip portion 530 of housing outer portion 508, and is additionally connected to bearing separating portion 512. Bearing separating portion 512 is additionally connected to second bearing 514. As such, first bearing 510 remains a constant distance d from second bearing 514.
In this state, lifting pin 118 is disposed below the top surface of ESC 106. As such, there is a space 538 between the top of pin holding portion 522 and shaft guiding portion 532.
A second state, a wafer-lifting state, of pin lifting system 116 will now be described with reference to FIG. 6.
To lift lifting pin 118 out through pin opening 546 of ESC 106, a lifting arm (not shown) engages and pin holding shaft 504 through window 518 at notch 520. Pin holding shaft 504 is continually lifted until seat portion 526 is separated from first bearing 510 and the top of pin holding portion 522 reaches the top of shaft guiding portion 532.
The problem of a lifting pin damaging an ESC, for example as discussed above with respect to FIG. 4, will now be described as applied to pin lifting system 116, with reference to FIGS. 7-10.
FIG. 7 is an exploded view of portion B of FIG. 5. In the figure, end portion 528 of pin holding shaft 504 does not actually touch first bearing 510. End portion 528 is spaced a distance 702 from first bearing 510. Pin lifting system 116 is designed in this manner to provide friction free movement along the axis parallel with the length of pin holding shaft 504.
FIG. 8 is an exploded view of portion C of FIG. 5. In the figure, end portion 528 of pin holding shaft 504 does not actually touch bearing separating portion 512. End portion 528 is spaced a distance 802 from bearing separating portion 512. Pin lifting system 116 is designed in this manner to provide friction-free movement along the axis parallel with the length of pin holding shaft 504.
The outer diameter of pin holding shaft 504 is conventionally designed to be as close to the inner diameter of each of first bearing 510 and bearing separating portion 512 to limit lateral movement of pin holding shaft 504. However, as discussed above, in order to provide friction-free movement of pin holding shaft 504, gaps still remain. These gaps may lead to a tilting of lifting pin 118, as will be described with reference to FIGS. 9 and 10 below.
Presume that arrow 902 of FIG. 9 represents the ideal longitudinal axis of pin holding shaft 504, wherein the longitudinal axis of lifting pin 118 is normal to the upper surface of ESC 106. In this example, further presume that pin holding shaft 504 is actually tilted such that end portion 528 touches bearing separating portion 512 at point 550, as illustrated in FIG. 5, whereas end portion 528 additionally touches first bearing 510 at point 552. In such a case, the longitudinal axis of pin holding shaft 504 actually is parallel with arrow 904 of FIG. 9. In this example, therefore, pin holding shaft 504 is tilted by an angle φ.
As discussed above, the distance d is the distance between first bearing 510 second bearing 514. The spacing Δ1 906 is the spacing between end portion 528 and first bearing 510, which is additionally illustrated as distance 702 in FIG. 7. As such, in FIG. 9, distance d and spacing Δ1 906 are related to angle φ as:cos φ=Δ1/d.  (1)Therefore, with a known distance d and spacing Δ1 906, the maximum tilt angle φ of pin holding shaft 504 may be calculated.
Once the maximum tilt angle φ of pin holding shaft 504 is calculated, the maximum, unwanted, lateral displacement of lifting pin 118 may be determined. Returning to FIG. 5, distance D is the distance from the upper surface of ESC 106 to point 550, where end portion 528 touches bearing separating portion 512. Using maximum tilt angle φ of pin holding shaft 504 and the distance D, the maximum lateral displacement of lifting pin 118 may be determined.
As illustrated in FIG. 10, presume that arrow 1002 represents the ideal longitudinal axis of pin holding shaft 504, wherein the longitudinal axis of lifting pin 118 is normal to the upper surface of ESC 106. In this example, further presume that pin holding shaft 504 is tilted the maximum tilt angle φ. In such a case, the longitudinal axis of pin holding shaft 504 actually is parallel with arrow 1004 of FIG. 10. Further, the maximum lateral displacement of lifting pin 118 is Δ2 1006. As such, distance D and maximum tilt angle φ are related to Δ2 1006 as:Δ2=D cos φ.  (2)Therefore, with a known distance D and known maximum tilt angle φ, spacing Δ2 1006 may be calculated.
Plugging equation (1) into equation (2), yields:Δ2=(D/d)Δ1.  (3)Therefore, it is clear that the maximum lateral displacement Δ2 of lifting pin 118 is directly related to the proportion of the distance D from the upper surface of ESC 106 to point 550 to the distance d between first bearing 510 second bearing 514.
As an example, presume that in a conventional pin lifting system, the distance d between first bearing 510 second bearing 514 is 1.2 cm, the distance D from the upper surface of ESC 106 to point 550 is 4.4 cm and the spacing Δ1 between end portion 528 and first bearing 510 is 1.4 mm. In such an example, the proportion of the distance D from the upper surface of ESC 106 to point 550 to the distance d between first bearing 510 second bearing 514 is 3.6. Using equation (3), the maximum lateral displacement Δ2 of lifting pin 118 is calculated to be 5.1 mm. In other words, lifting pin 118 has 5.1 mm of unwanted lateral play, with which lifting pin 118 may contact and damage ESC 106.
What is needed is a pin lifting system that decreases the lateral displacement of the pin.